Don't trigger filter_map_identity with an iterator from an empty array

[lapla-cogito]

fix #12653

changelog: [filter_map_identity]: don't lint for creating an iterator from an empty array

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[samueltardieu]

Couldn't we suggest using {std,core}::iter::empty::<T>() instead?

[Jarcho]

Thank you.

[Jarcho]

iter::empty would be close enough to the same thing (different type, but close given the array length is part of the type). Could arguably be a different lint though that catches different ways of writing an empty iterator.